Take this for what its worth, but using too small a grip will tend to make you grip the racquet harder and cause fatigue. Too big of a grip can limit wrist movement and also cause fatigue. I could never really judge the best grip size for me based on the "finger test" so I hit demos ranging from 4 1/4 to 4 1/2 before deciding that 4 3/8 was my ideal size.

One thing I noticed when using a grip that was too small for me was that the racquet was more easily knocked around in my hand.

You really have to play test different sizes in my opinion. If you go too small, you can build it up with additional over wraps or whatever. You have to be careful not to build it up so much as to lose the feel of the bevels. If you go too big, well that's a different story.

Like to use your wrist? Then go smaller. Like to hit flat? Then go bigger. Like to volley? Bigger. It goes along with your playing style though you could use the guides as an initial starting point. FWIW, I use 4 1/2.

Serena Williams, Monica Seles, Berdych are known to use big grip sizes (4 1/2 with overgrips and 5/8). They hit flat and muscle the ball at times.
Pros like Nadal and who whip the ball like the smaller grips.
I hit very flat on both sides and prefer 3/8 or 1/2 with overgrip and have small hands. I hit for 1 month with 1/4 and had a lot of wrist pain.
My personal opinion is that also with handle shapes of Head and Volkl you need a small grip size, but round ones like Wilson and Yonex you can go bigger.

Grip size is totally subjective to the player. I feel like I get more control with a larger grip, especially with a 2hbh. A lot of players prefer smaller grips for more maneuverability and topspin, but some hardly notice a difference in playability. The biggest question is how you want it to FEEL.

I've played with a 4 3/8 grip size and the racquet would spin around in my hand on certain off-center shots. I also played with a 4 5/8 grip size for several months and developed severe tendonitis in my playing hand (required 3 months rest, steroids and physical therapy).

The mean grip size is higher for............... Well, it is obvious. In fact this whole post is obvious, maybe I should delete it.

Actually I should hijack the thread and drone on about how much of a genius Federer was to win Olympic gold in the doubles playing with a small grip, well, small for doubles. Mariarafael would do the same with Nadal if s/he could.....hey, Nadal is a tennis god as he doesn't even know what grip size he uses so he must be better than Federer ZZZZZZzzzzzzzzzzzz.

This thread is very timely for me. Measuring on the Wilson thing, I am between 4 3/8 and 4 1/2. I play an APDGT, so I actually replace the Syntec with Skin feel grip, then add an overgrip. That gets it to the perfect size. Thinking 4 1/4 might be right, I tried that but it did not work. The butt end was just too small.

Personally, I'd look at this link, because it not only takes into account length but also finger thickness.
This was the way we all measured, growing up.
In general, the trend has been to move one grip size smaller because of the increased spin players are using.

I grew up with the old school notion that you used the largest grip that was comfortable for you. I am sized at 4 1/2 but growing up I used 4 5/8 up until a couple of years ago when I turned 36. I now use 4 1/2. I have not really noticed any more spin potential for me. I hit fairly flat so that must be the case. The pressure is spread out over my entire hand now instead of at the fingertips.